The major objective of this research is to understand the mechanisms whereby the contractile properties of the myometrium can be altered in a cyclic manner under the influence of estrogen, progesterone and during pregnancy. We will study how the mechanical behavior, chemical composition and chemical processes from which energy is derived for contraction are integrated and specifically changed as a result of hormonal status. The length-tension, force-velocity and series elasticity of the myometrium under various hormonal conditions will be determined and compared. We will also determine the conditions under which crossbridges may be attached in the resting state, and the energy requirement for the maintenance of attached crossbridges at rest in the pregnant myometrium, and learn how this relates to its holding capacity; the chemical composition (ATP, ADP, PCr, Creatine, elastin, collagen, protein, actin, CPK) in the various hormonal states will be determined, as will the energetic requirements for force development and its maintenance and for work production, all in the way of understanding the way in which these factors are regulated, if at all, by the hormones. Finally, we will attempt to differentiate the influence of physical factors, such as stretch, from the hormonal effects on the myometrium.